PREPARATION OF DIASTEREOMERIC 3,4-O-PYRUVATE ACETAL-CONTAINING D-GALACTOPYRANOSE DERIVATIVES, STRUCTURAL ASSIGNMENT AND USE FOR OLIGOSACCHARIDE SYNTHESIS

Treatment of phenyl 1-thio- and allyl 2,6-di-O-benzoyl-D-galactopyrano sides 3 with methyl pyruvate and BF3.Et(2)O in various solvents gave - O-benzoyl-2-deoxy-2-phenylthio-beta-D-idopyranose (4) and the correspo nding diastereomers of 3,4-O-pyruvate acetal-containing galactosides 5 . The phenyl 1-thio-beta-galactoside R-5a and the allyl a-galactoside R-5b were both converted into methyl 3,4-O-[1(R)-(methoxycarbonyl) eth ylidene]-beta-D-galactopyranoside (9), the structure of which as well as that of 4 was confirmed by X-ray crystallography. Compound R-5a was converted into 5-[(benzyloxycarbonyl)amino]pentyl thoxycarbonyl)ethyl idene]-beta-D-galactopyranoside (18) by using the (2-chloroacetoxymeth yl)benzoyl (CAMB) group for the temporary protection of position 2. Gl ucosamination of 18 and subsequent deblocking of the intermediate disa ccharide gave -(1-->2)-3,4-(S)-pyruvate-beta-D-Galp-O(CH2)(5)NH2 (21) which represents a fragment of the Escherichia coli K 47 polysaccharid e.